This invention relates to optically testing the quality of reflective cylindrical surfaces and is specifically directed to a method and an apparatus which is capable of analyzing the entire cylindrical surface of an object under test.
Present day method and apparatus for testing cylindrical surfaces uses test plates made to test the quality of one axis or the other of a cylindrical surface. For example, a relatively narrow spherical test plate can be made which is the standard or gage for judging the cylindrical surface under test. This plate is then placed in contact with the cylindrical surface across its main axis and is moved to various points along the main axis of the cylinder to check optically for errors by forming fringe patterns. In another form of test, the entire surface of a cylindrical test plate is brought into contact with the entire surface of the cylinder under test. Errors in the surface under test will show optically as fringe patterns.
Another possibility for testing cylindrical surfaces is to utilize an output reference cylinder in the path of a collimated beam, such as a laser beam, directed to the cylinder under test. This system is very expensive and limited in wavefront quality and has not been commercially acceptable.
It is an object of this invention to provide an improved method and apparatus for testing cylindrical surfaces which is highly efficient, compact, relatively rugged, inexpensive, and produces an excellent contrast fringe pattern without the use of an external interferometer.